1. Field of the Invention
This invention pertains to a wedge deadend that maintains the tension in wires and cables. More particularly, it pertains to a wedge deadend that maintains the tension in optical ground wires and cables.
2. Existing Technology
Deadends are used to attach wiring and cables, such as optical cables, to support structures. One type of deadend known in the art is the bolted deadend, illustrated in FIG. 1. These deadends consist of a body 100, top keepers 101, bolts, washers, and other attachment hardware 102, for attachment to a tower or other support structure (not shown). The number of keepers and other associated hardware is determined by the size and strength of the cable being installed. In some cases the keepers 101 must be removed from the deadend in order to install the cable. The keepers 101 and the other attachment hardware 102 are loose, and can be dropped during installation. Additionally, this deadend is heavy, with numerous bolts that must be tightened and torqued in sequence. As a result, a bolted deadend is time consuming to install.
Another known type of deadend is the formed wire deadend 200, illustrated in FIG. 2. Formed wire deadends are difficult to install. Wrapping the formed wires 201 around the cable 202 requires a great deal of hand strength. Also, the installer's fingers often get pinched while wrapping the formed wires 201 around the cable 202, which normally requires gloves to be worn during installation. Furthermore, formed wire deadends can be very long. The installer often cannot complete installation at the support structure, and must leave the site of installation in order to access the end of the deadend. As a result of this length, formed wired deadends can become excessively bulky and heavy. Furthermore, accurate alignment, which often takes a great amount of time, must be maintained between the bundles of wire.
A third type of deadend known in the art is the fiber optic clamp 300, illustrated in FIG. 3. These deadends have bolts 301 that must be tightened and torqued in sequence. This process is time consuming, and installation torque must be achieved to obtain the required holding strength.
A fourth type of deadend is the wedge deadend 400, illustrated in FIG. 4. These deadends use opposed wedges 401 and 402 positioned in a support structure 403 in order to hold a wire. As described in U.S. Pat. No. 5,647,046 (“Wedge Deadend to Support Aerial Cable”), a wedge deadend is both lighter and easier to assemble and install than the above-described alternatives.
However, existing wedge deadends are not capable of supporting Optical Ground Wire (“OPGW”) cables, which have some fundamental differences over the aerial cables held by U.S. Pat. No. 5,647,046. First, OPGW cable has “Reel Set” when it comes off the cable reel. That is, the cable retains the curvature of the reel even after it is unwound. Depending on the size (diameter) and construction (i.e.: alumoweld steel strands, alloy strands, aluminum pipe, stainless fiber tubes, etc.), OPGW cable can be difficult to straighten for installation.
Secondly, if a deadend is to have a wedge device to grasp the cable, the wedge must be designed to remain in place after installation. During use, the cable will experience forces from wind, snow, thermal expansion, and so forth. These forces cause vibration, cable motion, and loading, such that the OPGW cable will exert force which may loosen the wedge. The design of the wedge must therefore be self-locking.
For a wedge to be self-locking, it must have an angle similar to a “Jarno Taper” with a very small angle. A Jarno Taper is used on drills, reamers, etc. for remaining tight while still being easily removed. The problem of having a wedge with a very small angle is the “length of travel” necessary to open the grooves sufficient to accept the cable. Limiting the deadend's length limits the wedge travel and opening. This problem, and the “reel set” mentioned above, makes the top wedge difficult to advance to its proper position on the OPGW cable for loading and tensioning. Both wedges must align in order for the deadend to be properly installed. An offset in the wedge alignment will cause a stress point and a bend location, which can damage and eventually break the cable. To ensure the final location of the wedges is aligned, it is necessary to have both wedges advance evenly and together when the cable is tensioned. Therefore, it is necessary that both wedges be able to “grab” the cable.
If the above problems of reel set and the angle of the wedges keep the wedges from being aligned, it is left to the installer to force the top wedge into the installation position, through use of fingers, screwdrivers, rods, etc. This forcing could cause damage to the cable or the installer's hands.
Furthermore, it is necessary for the wedges to create the proper “squeeze” on the cable to advance the wedges together when the cable is tensioned. Otherwise the wedges will not “grab” the cable. That is, the cable could slip and not be retained. Proper wedge pressure on the cable is therefore required to ensure proper installation.